Photolithography or optical lithography is generally known as a process that is used in micro fabrication to selectively remove parts of thin films on a substrate. Photolithography generally uses a directed light source to transfer a geometric pattern from a photomask to a light-sensitive chemical resist material that is deposited on the substrate, thus generating an exposure pattern in the resist material from the light. A series of chemical treatments may then be used to etch or otherwise transfer the exposure pattern into one or more thin film layers positioned underneath the resist layer.
More recent lithography-type systems for micro fabrication operate to transfer or generate an exposure pattern in a resist layer without the intermediary step of creating a photomask. For example, a direct-write (DW) exposure tool operates to write patterns directly into one or more layers on a substrate (without a mask). The pattern is generally written from an electronic or computer-type file that is used to control a precision exposure source that may be selectively directed onto the layers of the substrate. More particularly, a DW exposure tool is generally configured such that the exposure of a circuit pattern is made not by illumination of the photo-resist through a mask or film negative of the circuit, but rather by directly and selectively exposing the desired areas of the resist or other layer on a substrate with a focused beam of the appropriate energy and dosage to create the desired circuit pattern.
An exemplary DW system is illustrated in FIG. 1. The DW system 100 generally includes an exposure unit 104 (EXU), which generally includes at least one energized beam, such as photon, electron, or ion beam that generally passes through at least one imaging head configured to focus the beam onto a recording medium on a substrate. The exemplary system 100 may also include a data-processing unit 102 (DPU) that is configured to read patterning data from a data storage medium, which may be within the DPU 102 or remotely positioned and in communication with the DPU 102. The DPU 102 takes the patterning data and loads it into its memory, generates a pattern writing instruction set, and sends the writing instruction set to the EXU 104. Depending on the form of the stored patterning data, when the patterning data includes an EXU writing instruction, the function of the DPU is reading, loading, and sending, as noted above. However, when the stored pattern data is a raw GDS-type file from a circuit designer, then the DPU 102 may also perform proximity correction and transformation to writing instruction instructions for the EXU 104. Alternately, the proximity correction and transformation can be performed separately by a standalone module. The EXU 104 receives the writing instruction from the DPU 102 and converts the writing instruction into control signals that are used to control the writing beam to write the pattern onto the substrate.
Substrates are sequentially loaded into the system 100 via an input cassette 108 by a substrate transfer mechanism (not shown). The substrate(s) are sequentially processed in the EXU 104 and are then unloaded from the EXU 104 by another substrate transfer mechanism (not shown). The processed substrates are positioned in an output cassette 106 and are generally positioned in the output cassette 106 in the same order the substrates were positioned in the input cassette 108. For example, the substrates in the input cassette 108 are generally removed sequentially, i.e., Lot 1, Wafer/substrate 1 (L1W1) is removed and processed first, and then Lot 2, Wafer/substrate 2 is removed and processed second. This process generally continues until each wafer/substrate in the input cassette 108 has been processed and positioned in the output cassette 106.
Although direct-writing EXU systems are efficient in that they generally eliminate photolithographic masking steps from semiconductor processing, there are several disadvantages to direct-writing EXU systems. For example, given the size (in memory space required) of the patterning data and the writing instruction, the DPU is often very large and expensive as a result of the memory and processing power required to work with the patterning data and writing instructions. More particularly, in order for an EXU system to operate efficiently, generally the DPU for the system will be capable of processing data in multiple terra bits per second, i.e., over 1000 gigabits per second. This magnitude of processing inherently generates heat and requires cooling to prevent failure of the processing mechanisms of the DPU. Additionally, the large processing power and memory required to process the patterning data and writing instruction is very expensive.
Therefore, in view of the challenges presented by DPUs of EXU systems, it would be desirable to have an EXU system that utilizes multiple EXU modules controlled by a single DPU.